1. Field of the Invention
The present invention relates to a magnetic composite, a method for producing the magnetic composite, and a shielding structure.
2. Description of the Related Art
In recent years, the operating frequency of electronic devices has been increasing higher and higher. Thus, an important challenge is how to effectively shield against or suppress electromagnetic noise emitted by such electronic devices and signal noise on transmission paths in the electronic devices. As known noise suppression means, a metal sheet or a sheet comprising a resin composition containing magnetic powder is used as a shield against electromagnetic noise and signal noise (see, for example, patent document 1 below).    Patent document 1: Japanese Patent Laid-Open No. 2005-209686    Patent document 2: Japanese Patent Laid-Open No. 7-204798
However, if a metal sheet is used as such noise suppression means, a change in ambient magnetic field causes an eddy current, which is disadvantageously likely to cause the metal sheet to be heated. Thus, the electronic device may be thermally affected or cooling means may become necessary. If a sheet containing magnetic powder is used, the volume fraction of the magnetic power (the content of the magnetic powder in the magnetic powder-containing sheet) needs to be maximized in order to enhance the effect of shielding against electromagnetic noise and the like. Then, the magnetic powders contact and connect to (couple to) one another, forming many percolation paths. As a result, an eddy current is generated as is the case with the metal plate.
To allow a possible eddy current to be inhibited, the volume fraction of the magnetic power may be reduced with an equivalent magnetic shielding effect maintained. To achieve this, a magnetic substance with a higher magnetic permeability is expected to be used. As such a high magnetic-permeability, an amorphous wire is known which is described in patent document 2 above and which is a thin metal wire.
However, as described in patent document 2 (Japanese Patent Laid-Open No. 7-204798), the amorphous wire is formed to be relatively long for manufacturing reasons. Thus, unlike in the case of the magnetic powder, mixing the amorphous wire with resin to form a resin composition is difficult. Consequently, it is difficult to form the amorphous wire into a sheet adapted to shield against electromagnetic noise and the like. Furthermore, instead of forming a sheet-like resin composition, connecting (laying out) long amorphous wires together (laid) so as to form a sheet is possible. However, in this case, ambient magnetic fields are expected to change to cause an eddy current as is the case with the metal sheet.
It is thus desirable to provide a magnetic composite capable of enhancing the effect of shielding against electromagnetic noise and the like (magnetic shielding effect) while inhibiting a possible eddy current, and a method for producing the magnetic composite, and a shielding structure comprising the magnetic composite.